The evolution of the market of fluid-managing systems in recent years has led to make increasingly efficient pumps, with the purpose of pressurising liquids and other fluids in general with the maximum possible efficiency, minimising the hydraulic losses and miniaturising the devices to the greatest possible extent. A classic response to these needs corresponds to the type of pump defined as gear pump, which has become increasingly popular in the market thanks to its characteristics of compactness, quietness, reliability and cleanliness, especially in the management of the fluid medium. Indeed, a gear pump allows keeping the fluid confined and isolated in a specific part of the pump body, close to the gears, with a guarantee of cleanliness of the fluid itself.
The advantage of being able to keep the fluid to be managed isolated has been further developed thanks to the advent of gear systems mechanically coupled to the motorised device that generates the rotary motion of such gears. This has caused the elimination of the direct contact of the fluid even with possible gaskets arranged on the drive shaft for driving the driving gear, which over time and for the most demanding applications can deteriorate and cause undesired losses of the fluid.
Gear pumps have been adopted in different technological fields, including applications that require extreme accuracy and reliability of distribution of the fluid. Consequently, gear pumps are widely used in medical apparatuses and in scientific instruments, as well as in professional equipment for ink printing.
Gear pumps are also used in the automotive industry. Gear pumps for automotive applications are characterised by different technical constraints, among which size, reliability, ease of assembly and efficiency. In particular, reliability concerns specific requirements of “long life”, resistance to vibrations and maintenance of performance in the absence of losses of the pumped fluid. In addition, there are the difficult environmental conditions in which these pumps operate. Consequently, these pumps must also possess characteristics of resistance to corrosion, as well as the ability to operate in a wide range of temperatures.
For the automotive applications one of the operative conditions in which the pumps must operate includes temperatures below the freezing point of the pumped fluid, typically consisting of water or other water-based liquids. As known, water and many water-based solutions tend to increase in volume in the liquid-solid change of state by freezing.
In a defined and closed volume, in which the expansion by freezing takes place, the static pressure can reach very high values. This pressure can cause substantial damage also to a pump that is directly coupled to a hydraulic circuit exposed to the freezing temperatures of the fluid.
In many cases, the simplest solution that can be proposed is to add a suitable anti-freeze liquid to the fluid to be pressurised, so as to move the freezing point towards lower temperatures. However, this solution is not always applicable, because by changing the composition of the fluid, other important chemical properties of the fluid itself are altered, with the risk of making it ineffective for the purpose of the application.
Therefore, there is the need for the pump to be designed with specific solutions that make it intrinsically immune to the increase in static pressure of the fluid due to freezing. For this purpose, some constructive provisions have been adopted in gear pumps.
For example, document WO 2009/029858 A1 illustrates a magnetically-driven gear pump in which, inside the pumping body, a predefined space is obtained where to house a particular element placed in direct contact with the fluid. This element is configured to absorb the increase in pressure of the fluid thanks to its own negative volumetric deformation. This element is typically manufactured with a compact elastomeric material having very low hardness, or with a closed-cell foamed material, for example silicone-based.
The purpose of the present invention is therefore to make an operating machine for non-compressible fluids and, more specifically, a gear pump provided with a system for compensating the internal pressures that is capable of solving the aforementioned drawbacks of the prior art in an extremely simple, cost-effective and particularly functional manner.